Synergistic effect of cathode and electrolyte additives on stabilizing the anodic interface for sodium-based dual-carbon batteries

Sodium-based dual-carbon batteries (SDCBs), as a novel energy storage device, have aroused increasing interest due to their low cost and the natural abundance of sodium. However, the application of such devices is currently limited by the low specific capacity and inferior cyclic stability, which is caused by the formation of an unstable anodic interface and significant crosstalk between anions and cations in the electrolyte. Here, we propose a dual-additive strategy employing Na2C2O4 as a cathode additive and fluoroethylene carbonate (FEC) as an electrolyte additive that effectively creates a stable anodic interface and suppresses anion-cation crosstalk. The as-constructed SDCBs with dual additives deliver good rate capability (30.9 mAh g−1 at 0.5 A g−1), excellent cyclic stability (∼81.9 % retention at 0.1 A g−1 after 280 cycles), and a high energy density of 192.6 Wh kg−1, which is superior to the performance of SDCBs with only one of the additives or without either additive. The anodic interface on the cycled anode becomes stable and uniform after the addition of the dual additives, and contains more Na-rich inorganic species and fewer organic species. The proposed strategy can improve the electrochemical performances of SDCBs and promote the commercial application of such devices thanks to the low cost, ease of operation, high safety, and environmental friendliness.